How can I tell how many objects I've stored in an S3 bucket?

Using AWS CLI

aws s3 ls s3://mybucket/ --recursive | wc -l 

or

aws cloudwatch get-metric-statistics \
  --namespace AWS/S3 --metric-name NumberOfObjects \
  --dimensions Name=BucketName,Value=BUCKETNAME \
              Name=StorageType,Value=AllStorageTypes \
  --start-time 2016-11-05T00:00 --end-time 2016-11-05T00:10 \
  --period 60 --statistic Average

Note: The above cloudwatch command seems to work for some while not for others. Discussed here: https://forums.aws.amazon.com/thread.jspa?threadID=217050

Using AWS Web Console

You can look at cloudwatch's metric section to get approx number of objects stored.

I have approx 50 Million products and it took more than an hour to count using aws s3 ls

There is a --summarize switch which includes bucket summary information (i.e. number of objects, total size).

Here's the correct answer using AWS cli:

aws s3 ls s3://bucketName/path/ --recursive --summarize | grep "Total Objects:"

Total Objects: 194273

See the documentation

Although this is an old question, and feedback was provided in 2015, right now it's much simpler, as S3 Web Console has enabled a "Get Size" option:

Which provides the following: